In recent years, a communication system which introduces femto-cell base stations has been developed more and more in order to improve the quality of communication area.
The femto-cell base station is a small radio base station which covers a narrow communication area defined by a radius of approximately several tens of meters, and is installed indoors within a home or an office with the intention to cover an indoor communication area. In this way, communication quality can be improved in communication areas which cannot be covered by existing micro-cell base stations. In addition, communication areas can be covered without incurring costs for the upgrading of infrastructure for micro-cell base stations.
In this regard, a communication system which introduces femto-cell base stations uses CS-dedicated PDG (Packet Data Gateway) which is a relay device for CS (Circuit Switching) services, and PS-dedicated PDG which is a relay device for PS (Packet Switching) services independently of each other.
FIG. 1 is a diagram showing an exemplary communication system which introduces a femto-cell base station related to the present invention.
In the communication system which introduces the femto-cell base station, a method has been contemplated to classify IP addresses of relay devices (PDG) connectable to networks 130a, 130b into CS-dedicated PDG 160 for CS services and PS-dedicated PDG 170 for PS services, and separately register these IP addresses in femto-cell base station (Femto AP) 120, as shown in FIG. 1. In the scenario shown in FIG. 1, “AAAA, BBBB” has been registered as the IP address of CS-dedicated PDG 160, while “CCCC, DDDD” has been registered as the IP address of PS-dedicated PDG 170.
Then, femto-cell base station (Femto AP) 120 connects to CS-dedicated PDG 160 based on the IP address “AAAA, BBBB” of CS-dedicated PDG 160 to provide CS services, or connects to PS-dedicated PDG 170 based on the IP address “CCCC, DDDD” of PS-dedicated PDG 170 to provide PS services.
However, in the communication system shown in FIG. 1, since the IP addresses of relay devices (PDG) must be registered in femto-cell base station (Femto AP) 120, the system will bear a larger load for IP address registration processing since a larger number of femto-cell base stations (Femto AP) 120 are installed in the system. Also, in the communication system shown in FIG. 1, when the IP address of a relay device (PDG) is changed, the IP address registered in femto-cell base station (Femto AP) 120 must be changed as well.
Because of these inconveniences as mentioned above, a need exists for the development of a system which is capable of separately using IP addresses for CS-dedicated and PS-dedicated relay devices (PDG) in a simple way.
For reference, as a technical document which has been filed prior to the present application, there is a document which discloses a technology that enables a public mobile terminal to utilize both public mobile communication services and internal services, while protecting SIP messages with IPScc (JP2008-228250A (hereinafter called “Patent Document 1”)).
There is also a document which discloses a technology related to standardization of 3PPP (3GPP TS 33.234 V8.0.0 (2007-12) (hereinafter called “Non-Patent Document 1”)).